High voltage and relatively high current capability solid-state switches, such as one described in an article entitled "A Field Terminated Diode" by Douglas E. Houston et al, published in IEEE Transactions on Electron Devices, Vol. ED-23, No. 8, August, 1976, and those discussed in pending U.S. patent applications Ser. No. 972,056, filed Dec. 20, 1978, and Ser. Nos. 972,021, 972,022, and 971,886, all filed Dec. 20, 1978 (now abondoned), and having a common assignee with the present application and U.S. patent applications Ser. Nos. 107,774, 107,773, 107,772, 107,780, and 107,775, which were all filed Dec. 28, 1979 with the present application and have a common assignee with the present application, have an ON (conducting) state and an OFF (blocking) state. These switches are capable of blocking relatively large potential differences in the OFF state. Each of these switches has two output terminals which are generally denoted as the anode and cathode, a control terminal which is generally denoted as the gate, and a semiconductor body whose bulk separates the anode, cathode, and gate regions. The parameters of the various portions of the semiconductor are such that with the potential of the anode region being greater than that of the cathode region and the potential of the gate region being insufficient to cause the potential of a vertical cross-sectional portion of the bulk of the semiconductor body between the anode and cathode to be greater in potential than the anode or cathode regions there is facilitated a substantial current flow between the anode and cathode regions via the bulk. With the potential of the gate region being sufficiently more positive than that of the anode and cathode regions to cause a vertical cross-sectional portion of the bulk of the semiconductor body between the anode and cathode regions to be more positive in potential than the anode and cathode regions there is facilitated an interrupting or inhibiting of current flow between the anode and cathode regions. The magnitude of the needed gate potential necessary to turn off these switches is a function of the geometry and doping levels of the semiconductor regions of each switch and of the anode and cathode potentials.
Control circuitry used to apply a blocking voltage to the gate terminal of each of these switches must be able to sustain a more positive voltage than is at the anode and cathode terminals and must be able to supply current which is generally of the same magnitude as flows through the anode and cathode of each switch.
U.S. patent applications Ser. Nos. 972,023 and 972,024, filed Dec. 20, 1978 (now abondoned), and have a common assignee with the present application, describe and illustrate control circuitry which itself uses a high voltage and current switch of the type described hereinabove to control the state of a similar switch. If a control circuit should fail to break (interrupt) current flow through on ON switch connected thereto, it is necessary to electrically disconnect the control circuitry from one of the supply potential sources. The control circuitry is then reset and reconnected to the potential source. It is then activated again so as to break conduction through the ON switch.
Usually a conventional high voltage and high current capability switch is used between the high voltage source and the control circuitry. This switch can be an optically activated switch. Generally it is a relatively expensive component and only one is used for a relatively large number of control circuits. If any of the switches to be controlled fails to turn off, it is necessary to disconnect all the control circuits from the power supply. This may result in all of the switches connected to the control circuitries being switched to the ON state independent of which state is desired. This is undesirable in some switching applications. The speed of operation and power dissipation of the above-described control circuitry may be slower and higher, respectively, than is desired in some switching applications.
It is desirable to have circuitry capable of controlling high voltage and high current solid-state switches of the type discussed hereinabove which has improved switching time and lower power dissipation than prior art circuitry, and which can maintain some switches connected thereto in the desired state even if one of the switches being controlled fails to break current (assume the OFF state).
Copending U.S. patent application Ser. No. 107,777, filed Dec. 28, 1979 with the present application and in which there is a common assignee with the present application, contains subject matter similar to that of the present application.